In variable print technologies, document sets are produced in which each document in the set is targeted or personalized to a different recipient, but all documents of the set may share some elements. Elements in the document may be categorized into three types, namely, fixed, reusable and unique. Fixed elements are used by each and every document in the set. Reusable elements are used by at least two but not all documents in the set. Unique elements are used only by one document in the set. The sharing of fixed or reusable elements may improve the efficiency of processing variable print documents because shared elements may be described, processed, and cached collectively in one action, thereby to reduce memory- and time-consuming redundancy.
Creation of variable print documents using state of the art authoring systems may rely on the use of a page layout tool and a method of specifying the logic of each document in the set. The logic may dictate the selection of reusable elements based on certain data in a database and certain business rules. The logic may also specify how to generate the unique elements, for example, a text element may contain a unique address of a recipient.
The output of such authoring tools is a print stream in a standard format describing the pages to be printed. The commonly used formats for printing such jobs efficiently describes the documents in the set in terms of the elements that make up the document. This improves the efficiency of the description in terms of file size as well as providing the necessary information for the printing system to perform further optimizations and caching. Examples of commonly used print stream formats that employ the methodology of describing documents in terms of reusable elements include Creo's proprietary Variable Print Specifications (VPS) format, Personalized Print Markup Language (PPML), for example, as defined by the Print On Demand Initiative, and Personalized Print Markup Language/Variable Data Exchange (PPML/VDX), developed by the Committee for Graphic Arts Technologies Standards (CGATS), and it was approved by the American National Standards Institute (ANSI) in 2002 and available from the Association for Suppliers of Printing, Publishing and Converting Technologies (NEPS).
The operation of authoring tools may be defined by the page layout space and the print stream space.
The page layout space describes the intended appearance of a page in terms of page elements, which may be created by a graphic designer using page layout tools such as, for example, Quark Xpress or Adobe InDesign. These page layout tools allow the designer to place, e.g., on a computer screen, a representation of the final page, rectangular frames, text boxes, raster images, and other shapes. The page layout application may be augmented by a dynamic document authoring tool that allows insertion of data or logic driven elements into the design space. For example, a name or address may be inserted to a text paragraph, or an image of a product may be dynamically inserted to an image box. The authoring tool may maintain the information on the nature of reuse of each element (for example, whether it is fixed, reusable or unique). The print stream space may describe the print job in terms of a set of elements (e.g., fixed, reusable or unique) and a set of page descriptions that make references to these elements.
In order for an authoring tool to produce its output, it is desirable to map the elements from the page layout space to elements in the print stream space and generate the page descriptions in terms of references. A basic mapping scheme may dictate that:
(a) For each fixed element in the print layout space, generate one corresponding fixed element in the print stream space.
(b) For each reusable element in the print layout space, there may be k different reusable elements in the print stream space, k being the number of different instances.
(c) For each unique element in the print layout space, there will be n different unique elements in the print stream space, n being the number of recipients, or number of instance documents in the set.
The authoring tool may use the basic mapping scheme to map most elements from the page layout space description of the document to the print stream. However, with an increased number of elements, the amount of processing may increase significantly. Moreover, with an increased number of overlapping elements, there is an increased amount of redundant or unnecessary processing because processing speed may be proportional to the total coverage area of all the elements in the document. Thus, using current techniques, a variable print document may often exceed the cache for the raster image processor (RIP) associated with the output device, e.g., the printer. A method and apparatus are therefore desirable for efficient processing of data in the production of variable print documents.